Re: I think my book may be wrong about cardinality, but I'm not sure

From: David Portas <>
Date: Tue, 24 Jul 2007 22:36:34 +0100
Message-ID: <>

"beginner16" <> wrote in message

> 2)
> Relationship between two entities is called binary connection or
> second degree relationship. But connection can exists between more
> than just two entities. Level of connection is determined by the
> number of different entity types that exist in a connection.
> Now as far as relational DB goes, don't tables have only binary
> connections ( second degree relationship )?

No. An N-degree table implements an N-ary relationship between attributes - attributes which may well identify other entities. Do not assume relationship = foreign key. A foreign key is just one type of constraint (not necessarily the only one) for enforcing referential integrity in RM.

David Portas 
Received on Tue Jul 24 2007 - 23:36:34 CEST

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